This invention relates to flat panel luminaires having embedded light guides for controlled light extraction. More particularly, this invention relates to flat panel luminaires having embedded light guides of irregular tetrahedral shape.
Numerous applications use optical fibers for illumination. A typical application involves multiple optical fibers or bundles to propagate light to an open end of the fiber. Other applications propagate light along the entire length of a light guide to extract light at intervals rather than provide light at only the terminal end of the fiber. Numerous approaches have been proposed to achieve such interval light extraction from optical light guides or fibers. However, each proposal has disadvantages that limit the application or render it impractical.
For example, a known light guide encloses a wave guide in a transparent sleeve or cladding that contains embedded light-reflecting particles or powders. The transparent sleeve or cladding has an index of refraction greater than the index of refraction of the wave guide. This higher index of refraction causes conversion of a light propagation mode to a cladding mode at the proximal end of the wave guide. This depletes beam intensity as the light traverses the full length of the guide. Furthermore, the suspension of particles or powders within the sleeve can cause excessive absorption of the light within the transmitting medium itself. To attempt to overcome the lack of light extraction control, discontinuities, such as cuts or air bubbles, which disperse the propagating light, are included at regular intervals. The introduction of these discontinuities at regular intervals along the core can be difficult to produce and may not allow for continuous light extraction.
Another known type of light guide uses a light transmission element containing light diffusing layers or elements. The diffusing layers are convex or concave and are used to extract light at a specific wavelength. The light diffusing layers can be arranged such that all layers have increasing density (but constant thickness) toward the distal end of the transmitting medium. This light guide uses discrete diffusing elements without consideration of the quantitative light extraction capabilities of these elements.
In another known light guide, the number of light scattering elements increases toward the distal end of the light conductor. The disadvantages of this and the previous light extraction device include discontinuity of the light sources and difficulty in correctly spacing and sizing the extraction elements to provide controlled light extraction from the light guide. Furthermore, the manufacturing and assembly of these devices is awkward and costly.
Another known device also uses discrete elements to extract light from an optical fiber in conjunction with a light panel. This device uses angular recesses and does not provide means to control quantitatively the light extraction. The result is that illumination from the downstream recesses is progressively lower.
Also known is the use of a “curve-linear” tapering of the cross-sectional area of a fiber optic, wherein the flattened surface is abraded or painted. The tapering of the fiber optic provides a way of illuminating perpendicularly to the face of the distal end of the fiber optic. Additionally, it is known to paint elongated triangular reflective stripes onto a plastic plate. This latter technique does not allow enough area for practical light emission for general illumination. The light injection end in both these known techniques does not provide enough distance for an even light flux and will result in the formation of bright spots at the injection end.
In yet another known device, a matrix of dots is applied on a substantially transparent material. The dots have increased diameters as they lay distal to the light-injecting edge of a flat panel. This method is again limited by the actual area of reflectance.
In sum, known devices and methods generally include two dimensional light propagation over a flat panel in which light output is limited by the area of the reflective coating or treatment.
In view of the foregoing, it would be desirable to provide a flat panel luminaire in which the limitations associated with emitting light along an entire length of a light guide are substantially, if not completely, overcome.